2.3 Earthquake Hazards and Safety

---

Vocabulary

---

Liquefaction: when an earthquake's violent shaking suddenly turns loose soft soil into the mud
Aftershock: an earthquake that occurs after a larger earthquake in the same area
Tsunamis: if the earthquake is strong enough, the water displaced by the quake forms large waves
Base-isolated buildings: a building designed to reduce the amount of energy that reaches the building during an earthquake

Outline

---

How Earthquakes Cause Damage

• Local Soil Conditions
  • when seismic waves move from hard, dense rock to loosely packed soil, they transmit their energy to the soil
  • loose soil shakes much more violently than the surrounding rock
  • the thicker the soil is, the more violently the shaking will be
    • this means that if your house is built on solid rock, the shaking will be less than the houses that are built on sandy soil
• Liquefaction
  • 1964, a powerful earthquake hit Anchorage, Alaska and cracked opened the ground
    • some of the cracks were 9 meters wide
    • some of the cracks were formed by liquefaction
  • liquefaction is likely to happen where the soil has too much moisture
    • as the ground gives way, buildings sink and pull apart
  • during the 1964 earthquake in Alaska, liquefaction
    • caused a landslide that swept thee entire housing development

Making Buildings Safer

• Choice of Location
  • location of the building affects the type of damage it may suffer during an earthquake
  • that housing development went down the cliff and into the sea
    • steep slopes appose to the danger of landslides
    • a filled piece of land can shake violently
    • people should always check what their surroundings is like
  • the farther the structure is, the less shaking there will be
• Construction methods
  • during an earthquake, a brick building or wood-frame building may collapse if it is not fixed
  • sometimes plywood sheets support frames of wooden buildings
  • to avoid damage caused by liquefaction is to build new homes on solid rock
  • bridges and highways dig down the soft soil and through the firmer ground
  • like the suspension of a car, the pads smooth the car from bumpy rides
    • during an earthquake, a base isolated building sways back and forth without any violent shaking
  • earthquakes indirectly cause floods and fire when the pipes break
    • automatic shut-off valves can be installed to cut off gas and water flow
• Aftershocks
  • sometimes after an earthquake, there is an aftershock
  • buildings that are weakened by an earthquake, collapse during an aftershock
    • depends when an aftershock might happen
  • aftershocks may strike in hours,days or even months
• Tsunamis
  • when an earthquake jolts the ocean floor, it starts to rise a little
  • it takes the water out of its way
    • if the earthquake is strong enough, the quake will start to form large waves
  • tsunamis spread out from an earthquake's epicenter and speeds across the ocean
    • the distance between the waves are 100 and 200 kilometers
    • some of the heights of the waves is about the height of a six-story building

Protecting Yourself During an Earthquake

• the main dager of protecting ourself is falling objects
• it means you need to crouch beneath a table and hold on to it so it won't fall
  • the table helps you protect from falling objects
• if there is no table near you, then go crouch down to an inner wall
  • cover your neck with your hands
• if you are outside, go to the middle of the street and stay out of the trees plus the electricity wires

Diagram

---